Short- and Long-Term Response of Deteriorating Brackish Marshes and Open-Water Ponds to Sediment Enhancement by Thin-Layer Dredge Disposal

Abstract

Artificial sediment enhancement using a thin layer of dredged material has been suggested as a means to increase elevation and create soil conditions conducive to increased marsh structure and function in deteriorating marshes. Using a chronosequence approach, we examined the effects of sediment enhancement in deteriorating marsh and open-water pond habitats located in six brackish marshes. Sediment enhancement of both marsh and interior pond sites had significant, immediate, and long-lasting effects on physical soil properties and nutrient status with increased bulk density and inorganic nitrogen. Vegetative cover and productivity response were minimal for deteriorating vegetated marshes with the short-term response data showing no significant impact of sediment enhancement and long-term trends indicating decreasing productivity over time. In contrast, trajectory models of vegetative cover and productivity in interior pond sites showed increases over time indicating that, for restoration of interior ponds, sediment enhancement may prove valuable. The use of trajectory models emphasizes the need for long-term monitoring to determine restoration success of projects.